1. Field of the Invention
The present invention related to a magnetic tape cartridge, and in particular to a magnetic tape cartridge and a single reel around which a magnetic tape with a leader pin fixed to the leading end thereof is wound and which is contained in the cartridge casing for rotation, having a latch spring removably mounted at the cartridge casing tape outlet opening, and the cartridge case opening is provided with an opening and closing slide door and lock.
2. Description of the Related Art
There has been known a single-reel magnetic tape cartridge as for example the type disclosed in Japanese Unexamined Patent Publication No. 11(1999)-242870, comprising a cartridge casing and a single reel around which a magnetic tape is wound and which is contained in the cartridge casing for rotation, as a recording medium for an external storage device for a computer and the like. In this type of magnetic tape cartridge, a leader pin fixed to the lead end of the magnetic tape is engaged by the lateral drawing force of a latch spring fixed in the tape cartridge casing, and is removably held in the cartridge casing.
FIGS. 23 and 24 show a vertical cross-section view and a fragmentary horizontal cross-sectional view, respectively of the structure of the pin holding portion contained in aforementioned publication.
In FIGS. 23 and 24, synthetic resin cartridge casing 4 is formed by upper half 2 and lower half 3, and a single reel (not shown) around which the magnetic tape, connected at the tail end thereof to leader pin 5, is wound. A tape outlet opening 8 for drawing out the magnetic tape is formed on one sidewall of cartridge casing 4, and tape outlet opening 8 is provided with a slide door 20, which is movable in the direction parallel with the side of cartridge casing 4. Slide door 20 is propped in the direction of the closed position of tape outlet opening 8 by a door spring (not shown).
A concave recess 9 for extracting leader pin 5 is formed adjacent to tape outlet opening 8 of cartridge casing 4, and a latch spring 30 is provided for removably holding leader pin 5 in recess 9 when the magnetic tape cartridge is not in use and the tape is in the completely wound state.
When the magnetic tape cartridge is installed in the record and playback apparatus of an external storage device slide door 20 opens, leader pin 5 is drawn out by a robot arm of the record and playback apparatus, and the magnetic tape is drawn out to the predetermined running position from which reading and writing data thereto are possible.
Leader pin 5, as shown clearly in FIG. 23, comprises a shaft-shaped tape clamp 5a at the center thereof, around which the lead end of the magnetic tape is wound and secured in place by fastening a cross-sectional C clamp 5e. Tape clamp 5a is connected at its upper and lower ends to a pair of thin plate-shaped flanges 5d, and on the outside of flanges 5d in the axial direction are a pair of small diameter portions 5b, which are caught by the robot arm of the playback and record system, which are spaced by a pair of column-shaped flanges 5c. 
Latch spring 30, as in the form shown in FIG. 25 for example, is formed of a plate spring pinched between respective upper and lower halves 2 and 3 of cartridge casing 4, and upper and lower flanges 5c of leader pin 5 are each inserted into respective recesses 9 on the upper and lower halves of cartridge casing 4 and removably held therein by latch spring 30.
As shown in FIG. 25, latch spring 30 is formed in a substantially U shape in plan and is symmetrical about the horizontal axis thereof, and comprises a vertical base portion 30a from the upper and lower ends of which extends a back plate 30c and a pair of arms 30b that extend substantially parallel to each other, on the free end portion of each arm 30b is provided a pin holding portion 30d. The area between upper and lower arms 30b is cut out, and arms 30b are formed so that only pin holding portion 30d is brought into abutment with flange 5c of leader pin 5. Each pin holding portion 30d protrudes in a mound-shape, and a rear inclined pin guide surface 31 is formed at the lead end thereof (FIG. 24). When leader pin 5 is held by the robot arm inserted into cartridge casing 4, at the first contact made with guide surface 31 by the outer circumference of flange 5c of leader pin 5, arm 30b of latch spring 30 presses against flange 5c and is resiliently deflected toward the side, and it is possible for leader pin to be inserted into recess 9. Having passed guide surface 31, flange 5c of leader pin 5, as shown in FIG. 24, is held against the inner wall of recess 9 by the resilient force of pin holding portion 30d, and with this type of latch pin, with the fastening of respective upper and lower halves 2 and 3 of cartridge casing 4, the upper and lower edges of base portion 30a and back wall 30c are pinched and fixed in place by respective upper and lower halves 2 and 3.
FIG. 26 provides detailed illustration of the state in which leader pin 5 is inserted from tape outlet opening 8 into cartridge casing 4.
Recess 9, which accommodates leader pin 5, is provided with straight-line shaped guide walls 9A and 9B, for guiding flange 5c of leader pin 5 into the back of recess 9, and a semi-spherical holding wall 9c, which is of a slightly larger diameter than that of flange 5c. 
Up until now, leader pin 5 has been designed so that the center axis S thereof passes through the center of the curvature of semi-spherical holding wall 9c in the back of recess 9 along a perpendicular center line L1 of the sidewall of tape outlet opening 8 of cartridge casing 4 and is inserted into the recess 9, and if flange 5c of leader pin 5 is brought into abutment with leader pin guide surface 31 of the free end of latch spring 31, flange 5c is drawn in, and by the pressure brought to bear against guide surface 31, arm 30b is deflected toward the side (left side of the Figure) whereby it becomes possible for leader pin 5 to be inserted into the back of recess 9, and flange 5c, which has been passed over guide surface 31 to the back of recess 9, is held by the resilient force of pin holding portion 30d of latch spring 30 in the holding wall of recess 9.
However, because there are instances in which, due to unevenness, etc. in the relative positions of the robot arm of the record and playback apparatus and the magnetic tape cartridge inserted therein, leader pin 5 is inserted into recess 9 in a state in which the center axis S thereof is off track to the left or right of center line L1 of recess 9, if recess 9 is widened on the tape outlet opening 8 side to and guide walls 9A and 9B are provided inclining surfaces opening toward the outward direction, even if leader pin 5 is inserted into recess 9 in a state in which the center axis S thereof is off-center with respect to center line L1, guide walls 9A and 9B are structured so as to guide flange 5c so that center axis S is directed toward the center of the curvature of holding wall 9c. 
However, because there is also unevenness in the relative positions of guide surface 31 of latch spring 30, as shown in FIG. 26, when inserted into recess 9 from the state in which flange 5c of leader pin 5 is guided on guide wall 9A on the latch spring 30 side, if guide surface 31 is only pressed against by flange 5c, because arm 30b of latch spring 30 will not be deflected toward the side, and a problem arises in that it is not possible for leader pin 5 to be inserted into cartridge casing 4.
Guide surface 31 of latch spring 30 has a predetermined angle α′ relative to parallel straight line L2 parallel to center line L1. Conventionally, α′ has been an angle of 55°. Note that because the angle between guide wall 9a of recess 9 on the latch spring 30 side and aforementioned straight line L2 is 10°, angle β′ between guide surface 31 and guide wall 9a on the latch spring 30 side is 45°.
Because of this, when flange 5c is in the state of being guided by guide wall 9A, there are cases in which when flange 5c is inserted into recess 9, a problem occurs in that arm 30b of latch spring 30 is not deflected to the side even if guide surface 31 is pressed against by flange 5c of leader pin 5.
On the one hand, there are a variety of latch springs available for use in holding leader pin 5 in recess 9 beside that of the form described above. However, when a latch spring is fitted to cartridge casing 4, depending on the type and attachment structure thereof, there is a difference in the amount of the leader pin holding portion at the lead edge of the latch spring that projects toward recess 9, and depending on the pin holding portion, the engaging strength thereof changes, and problems relating to instability in inserting and removing the pin arise.
In particular, when the latch spring fitted to upper half 3 and the latch spring fitted are separate parts, this is a cause of difference in the upper and lower engaging strength, and there is fear that leader pin 5 will tilt. In addition, if the amount of the pin holding portion of the latch spring that projects is small, the holding strength is weakened, and there is a chance that vibrations, etc. caused when magnetic cartridges are stored or shipped can cause leader pin 5 to be dislodged from recess 9, and conversely, if the amount of the pin holding portion that projects is large, there is a chance that the form of the latch spring will become deformed when magnetic tape cartridges are stored or shipped; in either case, faulty insertion and removal of leader pin 5 caused thereby give rise to the fear of diminished operational reliability.
FIG. 27 shows a possible type of construction of separate upper and lower latch springs. Latch spring 55 is formed of separate upper and lower wire spring members, provided with a pin holding portion 55a on the free end of each thereof that contacts leader pin 5, arms 55b extending from pin holding portions 55a in the direction opposite the tape outlet opening, and a base portion bent into a substantially L-shape and inserted into and fixed in a curved groove 56a of fixing portion 56 formed on the rear end portion of recess 25 on an inner wall of the cartridge casing, by which latch spring 55 is held in a predetermined position.
However, if the fixed position of latch spring 55 is supported only at the rear end position of arms 55b, which are the farthest removed from position at which leader pin is contacted, a microscopic displacement of fitting portion 55e of aforementioned fixing portion 55 has an effect on pin holding portion 55a, and the amount thereof that projects toward recess 9 of leader pin 5 changes, causing aforementioned weakening of engaging strength and instability in inserting and removing leader pin 5. Further, even if the fitting portion of the rear end of the arm portion of latch spring 55 is of a construction in which it is fixed to a projecting heat fused fixing portion, a displacement of the fitting portion of the fixing portion will cause the same change to the engaging power.
Also, in a magnetic cartridge of the type described above, if tape outlet opening 8 for extracting the magnetic tape is jarred open by a shock caused during shipping or storage thereof, or any other time it is not being used, because it is possible that foreign matter be inadvertently introduced to the inside of the cartridge casing, more than simply propping the slide door in the direction of the closed position by use of a door spring, but locking the slide door advantageously prevents inadvertent opening of the slide door and improves reliability.